Turpentine Broom
Thamnosma montana
Photographed in Wickenburg Mountains, Yavapai Co., Arizona. Sept. 6, 2008.
The fruits of turpentine broom have large, conspicuous oil glands emitting a very pungent odor on being pressed. Photographed in Wickenburg Mountains, Yavapai Co., Arizona. Sept. 6, 2008.
SHRUB: A meter tall hemisphere with many, smooth, yellow-green stems
radiating from base. In winter the smooth, leafless stems take on a
lemon-yellow cast - see photo below.
LEAVES: Leaves are elyptic, but soon deciduous leaving the smooth,
yellow-green stems to carry on photosynthesis. Stems and fruits all exude
pungent, citrus-like, terpenes when injured.
RANGE: In the Sonoran Desert this plant mostly appears in transition to
chaparral and is more common along the northern tier from Mojave Co. east to n.
Gila County. Also grows sporadically in the Mojave Desert of California and
Nevada, but then also in portions of the Chihuhuan Desert to the east. Its
abundance is often increased where cattle have been grazed to excess, because
they avoid it in favor of more palatable forage.
FRUIT: Misshapen, bilobed sphere is golden
yellow when mature with conspicuous oil glands. Dry with several seeds.
FLOWERS: The long, deep purple petals remain erect and confluent. Stan
Shebs has a close photo of the
flower on Wikimedia.
UNARMED. No thorns.
Rudkin's Swallowtail (Papilio polyxenes coloro) uses this plant
for its
caterpillar stage affirming the relationship between members of the citrus and
carrot plant families.
Rutaceae -- Citrus Family
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